Lectins heterologous expression in tobacco: a strategy for enhancing plant resistance to phytopathogenic fungi

Every year, 10-15% of the world's major agricultural crops are lost due to plant pathogens; 70-80% of these diseases are caused by fungi. Today, only a few classes of antifungals are available. In addition, the same antifungals approved for medical use have been widely used for agricultural purposes for decades. Plants have always been a source of molecules with therapeutic potential and still provide the active ingredients of a significant number of new drugs. Natural plant-derived compounds could be, therefore, a promising alternative to the antifungal agents used in agriculture today. Lectins (initially named agglutinins for their ability to agglutinate red blood cells) are natural proteins found across all biological kingdoms. These proteins bind specifically to carbohydrates and the variability in their binding sequences for a ligand is similar to that seen in the antibodies of the animal adaptive immune system. Vicia ervilia agglutinin (VEA) from bitter vetch, can inhibit biofilms of both Gram- positive and Gram-negative bacteria, which are responsible for chronic infections caused by non-healing wounds in humans. Wheat germ agglutinin (WGA) from Triticum aestivum interferes with the germination and development of the hyphae of fungi belonging to the genera Aspergillus and Penicillium, due to the binding between lectin and chitin in the fungal wall. Botrytis cinerea, Alternaria alternata and Fusarium oxysporum, are phytopathogenic fungi that can infect a wide range of plant species, causing significant agronomic losses. In addition, their reduced susceptibility to fungicides is a growing concern. We cloned the VEA and WGA genes into vectors for constitutive plant expression and transformed Nicotiana tabacum plants. Having verified protein expression by Western blotting with specific antibodies, we are currently testing transgenic plants for increased resistance to A. alternata, B. cinerea and F. oxysporum by verifying both fungal growth and spore germination.